Building products

ABSTRACT

A method of manufacturing a building product from a mix ( 6 ) including particulate material and a thermoplastic binder which comprises heating the mix at least to a temperature at which the thermoplastic binder in the mix liquefies, subjecting the heated thermoplastic mix to a pressing action that shapes the heated mix, and cooling the shaped heated thermoplastic mix to solidify the thermoplastic binder and form the product (FIG.  4 ).

This invention relates to building products, more particularly but notexclusively for use in, and for, the building, construction and civiland structural engineering industries.

Concrete building products, such as masonry, paving, paving flags,paviours, flagstones, blocks, bricks, tiles, slates, posts, lintels,sills, slabs and panels and claddings and linings for walls, ceilings,roofs and floors have been made for many years for pressing or mouldingprocesses. Hereinafter such pressing or moulding processes will begenerically referred to for convenience as “pressing”. Concrete productsare typically made of a mix including fine particles such as sand,coarse particles such as an aggregate, a cement binder, a filler andwater etc. with the aggregate or alternatively a pigment providingcolour to the concrete product.

A typical pressing process involves the use of what is commonly known asa static block making machine. Pallets made from metal, plastics or woodare fed by a conveying means into the block making machine whichcomprises a mould, a concrete mix filling means one or more compactingdevices, optional vibration devices, a stripping device, and an outgoingconveying means. The pallet, which forms the profile of one side of theblock, is located under the mould in the machine. The mould comprisesone or more side walls each defining a side of the desired block, andpreferably the compacting and stripping device forms the final side ofthe block. Once the pallet has been located, the mould is lowered on tothe pallet and held in frictional contact to define a mould cavitycomprising the upper surface of the pallet, and the surfaces of thesidewalls of the mould.

The mould cavity is then filled with a concrete mix of the desiredcomposition optionally using vibration or other levelling means toachieve a desired profile of concrete. A compacting head, whichpreferably will also be used for stripping, is then lowered on to theupper surface of the concrete mix in the mould cavity and the concretemix is compacted by the force exerted by the compacting head, such forcebeing direct pressure and/or vibration to shape and form the product.Optionally, the mould cavity is then filled with a second concrete mixof another desired composition again optionally using vibration or otherlevelling means to achieve a desired profile of concrete mix. The use oftwo filling operations allows the manufacture of a block which primarilycomprises a strong cost effective non-visible layer in use and a morepleasantly aesthetic visible layer in use that may contain moreexpensive ingredients.

The compacting forces are stopped and the mould is then raised from thepallet with both the pallet and the compacting head, now acting as astripping device, being held in stationary alignment. When the mould hasbeen raised clear of the green (uncurred) concrete block thecompacting/stripping head is also raised clear of the green concrete.The formed green concrete block is then conveyed out of the block makingmachine on the pallet on which it was formed.

Optionally, the formed green concrete block on its pallet is conveyedinto a secondary processing area, such as a washing station, to effectan exposed aggregate finish and then into an area where it is allowed tocure to a hardened state. Having cured to a sufficiently hardenedstrength the block is then optionally transported to another secondaryprocessing area where it is subjected to the action of secondaryprocessing apparatus such as a shotblasting machine, bush hammer, chainflailer or the like and then into an area where it is packaged fordelivery. In some cases the depalleted blocks are put into yard storagefor a period of time before returning to a secondary processing area.The pallet is conveyed back into the block making machine and the makingcycle restarts.

Many other presses, pressing processes, apparatus and machinery andsecondary processes and processing machinery, other than thosedescribed, are available. By way of example, hermetic pressing machines,hydraulic pressing machines that require no vibration, hammer actionpresses, presses using stamper plates, and presses with roller actionare all used to make the same product type.

GB 947,917 describes a method of making hardened moulded bodies such asblocks, tubes, briquettes, or paving slabs by mixing of solid granularand or pulverulent mineral particles such as stone, ore, or coal with apreferably soft bitumen as binder by coating the individual solidparticles with a thin film of bitumen having a thickness of about 10μ orless, said method including the steps of moulding the bituminous mix bycompacting pressure applied at such conditions that in the mouldedbituminous body a void space of from 5 to 30% by volume of the mass isretained, and thereafter exposing the formed body to action of air at atemperature of from 300 to 600° F. to harden the bitumen in the body.

The production of cement is a costly process involving a significant useof energy since it involves the calcining of limestone. Furthermore, thecalcining of limestone liberates carbon dioxide and in total themanufacture of 1 tonne of cement is accompanied by the liberation of 1tonne of carbon dioxide to atmosphere. Accordingly, the inventors haveinvestigated ways of replacing the cement binder of conventionalconcrete with a binder which can be produced without the disadvantagesinvolved in the production of cement and yet enables the use of existingequipment and methodological for producing concrete products.

Accordingly, the-present invention provides a method of manufacturing abuilding product from a mix including particulate material, and abinder, characterised by the binder being a thermoplastic binder, whichcomprises heating the mix including the thermoplastic binder at least toa temperature at which the thermoplastic binder in the mix liquefies,subjecting the heated thermoplastic mix to a pressing process thatshapes the heated thermoplastic mix, and by cooling the shaped heatedthermoplastic mix to solidify the thermoplastic binder and form thebuilding product.

The thermoplastic binder of the present invention may be a polymericmaterial, for example polyethylene, polyurethane, or polyvinylchloride.However, in a preferred embodiment of the present invention thethermoplastic binder is a bituminous binder, more preferably anasphaltenes-containing binder having a penetration of less than 15 dmm.

Accordingly, the present invention further provides a method ofmanufacturing a building product from a mix including particulatematerial and a binder, characterised by the binder being anasphaltenes-containing binder having a penetration of less than 15 dmm,which comprises heating the mix including the asphaltenes-containingbinder to a temperature at which the asphaltenes-containing binder inthe mix liquefies, subjecting the heated asphaltenes-containing mix to apressing action that shapes the heated mix, and cooling the shapedheated asphaltenes-containing mix to solidify the asphaltenes-containingbinder and form the building product.

Asphaltenes are constituents of bituminous materials which are solublein carbon disulphide, but not in petroleum spirit. Typically,asphaltenes constitute 5% to 25% of a bituminous material (page 90 ofthe Shell Bitumen Handbook September 1991), the remainder of abituminous material comprising constituents such as resins, aromaticsand saturates, which are collectively referred to as maltenes. Thepresence of asphaltenes can be established using test method IP143/96.

The penetration of the asphaltenes-containing binder according to thepreferred embodiment is measured according to ASTM D5 at 25° C.Preferably the asphaltenes-containing binder has a penetration of lessthan 15 dmm, more preferably of from 1 dmm to less than 15 dmm.

Preferably, the asphaltenes-containing binder has a penetration of atmost 10 dmm, more preferably less than 10 dmm and most preferably lessthan 8 dmm. Further, the binder preferably has a penetration of at least1 dmm at 25° C., more preferably at least 2 dmm, more preferably atleast 4 dmm. The penetration values below 2 dmm can be measured bymeasuring at 40° C. and subsequently extrapolating the results to 25° C.

The asphaltenes-containing binder according to the preferred embodimentpreferably has a softening point measured according to the ring and balltest of ASTM D 36, of at least 50° C., more preferably at least 70° C.,even more preferably at least 100° C. Further, the binder preferably hasa softening point of at most 157° C., more preferably at most 150° C.,even more preferably at most 130° C.

The asphaltenes-containing binder of the preferred embodiment can beprepared in any way that is well-known to someone skilled in the art,provided that the binder obtained has the required hardness.

A process by which an asphaltenes-containing binder may be prepared isdeasphalting, more particularly propane deasphalting. In this process, aresidue from distillation of crude oil is treated with solvent undercontrolled conditions such that bitumen binder is precipitated. Thesolvent preferably is propane, propane-butane mixtures or pentane. Mostpreferably, the solvent is propane. The residue is usually residue froman atmospheric distillation tower. The process is primarily used forcrude oils of relatively low asphalt content. The process can suitablybe carried out as a countercurrent liquid-liquid extraction. Furtherdetails of the process are well known to someone skilled in the art.Suitable processes have been described in Kirk-Othmer Encyclopedia ofChemical Technology, Volume 3, pages 297-298.

The asphaltenes-containing binder of the preferred embodiment preferablycontains (i) from 15 to 95% by weight, based on total binder, ofasphaltenes, as determined according IP 143/96, which asphaltenescontain at least 60% aromatic carbon, and (ii) from 5 to 85% by weight,based on total binder, of further hydrocarbons as determined accordingIP 143/96. The percentage of aromatic carbon atoms present in theasphaltenes is measured by separating off the asphaltenes in the binderas described in IP 143/96, dissolving a sample of the asphaltenes incarbon disulphide or chloroform and assessing the percentage of aromaticcarbon by ¹³C NMR.

The asphaltenes comprise hydrogen, carbon and optionally other atoms.Specifically, the asphaltenes can contain up to 15% by weight of atomsother than hydrogen and carbon, more specifically sulphur, nitrogen andoxygen, preferably at most 12% by weight, most preferably at most 10% byweight, based on asphaltenes.

Generally, the further hydrocarbons present in the above preferredbinder, can contain up to 15% by weight of atoms other than hydrogen andcarbon, more specifically sulphur, nitrogen and oxygen, preferably atmost 12% by weight, most preferably at most 10% by weight, based onfurther hydrocarbons.

Preferably, the asphaltenes-containing binder contains at least 20% byweight of asphaltenes, based on total binder. More preferably, thebinder contains at least 25% by weight of asphaltenes. The amount ofasphaltenes is preferably up to 95% by weight, more preferably up to 70%by weight, more preferably up to 60% by weight, more preferably up to50% by weight, more preferably up to 45% by weight, most preferably atmost 40% by weight.

The asphaltenes-containing binder containing (i) from 15 to 95% byweight of asphaltenes-containing at least 60% aromatic carbon, and (ii)from 5 to 85% by weight of further hydrocarbons, may be prepared bysubjecting hydrocarbons to thermal cracking. Preferably, a residualhydrocarbon fraction is subjected to thermal cracking. The thermallycracked product can be used as such, or in combination with any otherhydrocarbon fraction as long as the required hardness is achieved.

Preferably, the asphaltenes-containing binder consists at least partlyof product obtained by subjecting hydrocarbons to thermal cracking. Mostpreferably, the binder consists of product obtained by subjectinghydrocarbons to thermal cracking. Although in such case part of thethermally cracked product can be used, the binder only contains productwhich has been thermally cracked.

Thermal cracking is preferably carried out by pre-heating a hydrocarbonfraction to a temperature from 350 to 500° C., maintaining thepre-heated oil at such conditions as to cause thermal cracking andsubsequently separating off one or more light fractions. Thermalcracking of residual fractions usually involves a temperature of between300 and 600° C. The pressure can be in the range from 1 to 100×10⁵ N/m²(bar), preferably in the range from 2 to 20×10⁵ N/m² (bar). Thermalcracking is preferably carried out in a soaker. The thermally crackedproduct as such can be used as binder, or the binder can be only a partof the thermally cracked product. In the latter case, the binder isseparated from the thermally cracked product in any suitable way.Preferably, the binder is produced by separating off the light fractionsby flash distillation, more preferably by vacuum flash distillation.

Another process by which the asphaltenes-containing binder can beobtained comprises subjecting a residual fraction to hydroconversion ata temperature in the range from 200 to 450° C. and a pressure in therange from 50 to 200×10⁵ N/m² (bar), optionally preceded byhydrodemetallization. Preferably, the hydroconversion ishydrodesulphurization.

In the method of the present invention it is preferred to use bituminousbinders, in particular asphaltene-containing binders having apenetration of less than 15 dmm as the thermoplastic binder of thepresent invention, as building products prepared using these bindersdisplay, amongst other attributes, excellent flexural strength,compression strength, impact and crack resistance, and are substantiallywater-proof.

The particulate material to be used in the method of the presentinvention may in principle be of any type of particulate material, forexample mineral particles, cement, concrete, dust, recycled asphalt,recycled tyres, clay, old sand, porous particles such as zeolite andperlite, crushed shells, shells, organic waste such as leaves and bones,fly ash, wood particles such as chips, flakes, etc. Preferably, theparticulate material is in the form of mineral particles.

Preferably the particulate material employed in the method of thepresent invention is a combination of particles having a particle sizeof at most 63 micrometers (so-called filler) and particles having aparticle size in the range from 63 micrometers to 2 mm (so-called sand)and particles having a particle size in the range from 2 to 8 mm,preferably from 4 to 8 mm (so-called stones or aggregates), optionallyin combination with particles having larger sizes. The particle sizesare measured by sieving with sieves having openings of the indicatedsize. Preferably, the amount of each of filler, sand and stones is inthe range from 10 to 50% by weight, (the combination to total 100% byweight) based on total amount of particulate material. Particulatematerials having a particle size of more than 8 mm are preferablypresent if larger objects are made. Accordingly, in a preferred methodaccording to the present invention the particulate material includessand aggregate and filler.

The temperature at which the thermoplastic binder in the mix liquefiesis dependent upon the softening point of the thermoplastic binder beingemployed. Where the thermoplastic binder is a asphaltenes-containingbinder the temperature at which the asphaltenes-containing binderliquefies is preferably at least 50° C., more preferably at least 70°C., even more preferably at least 100° C.

By means of the invention, the liquid phase of the thermoplastic binderacts like water to lubricate and bind the particles of the thermoplasticmix together during the pressing process thereby avoiding the use ofwater which is necessary in addition to the cement binder with concretemixes. Moreover, the thermoplastic binder enables a building product tobe simply and easily produced using existing apparatus, thereby avoidingthe costs of new plant and machinery. Where the thermoplastic binder isa bituminous binder, the liquid phase of the binder is the maltenephase.

Accordingly, a preferred method according to the present invention is amethod wherein the liquid phase of the thermoplastic binder lubricatesand binds during the pressing action.

The inventors have coined the term ‘hybrid’ to qualify the completelynew building products prepared by the present invention because athermoplastic binder, which is a synthetic or bituminous material, wouldhitherto have been thought of as a non-compatible material to use forthe manufacture of concrete building products which are traditionallymade from natural materials and use pressing, but not pressing and heat,to shape and form the product. The mix can also be termed—‘hybridthermoplastic mix’ because it includes a synthetic thermoplasticmaterial and natural materials such as sand, aggregate, fillers etc.

Unexpectedly, not only does the method of the invention work to producesimple building products in the form of blocks, the invention is capableof producing a wide a variety of building products including masonry,paving, paving flags, paviours, flagstones, blocks, bricks, tiles,slates, posts, lintels, sills, slabs and the like, which has hithertobeen achieved with traditional equipment and methodologies. Examples ofbuilding products which may be conveniently prepared by means of thepresent invention are construction elements as described on page 16,lines 28 to page 17 line 25 of WO 00/46164.

By definition a thermoplastic material softens when exposed to heat,liquefies when the temperature is elevated beyond the materials meltingpoint, and returns to its original condition when cooled to ambienttemperature.

When the thermoplastic mix, containing the thermoplastic binder isheated, conveniently in a supply hopper, the liquefied thermoplasticbinder forms a coating around the aggregate, sand and fine fillerparticles and the heated thermoplastic mix is transferred from thehopper to a cavity of a mould forming part of a pressing apparatus suchas a block making machine.

Preferably, in order to produce a more cost effective hybrid buildingproduct, the proportion of the particulate material such as sand,aggregate, fillers etc. is greater, and desirably far exceeds, theproportion of thermoplastic binder because the particular materialportion of the thermoplastic mix is the lowest cost material employed.Expressed in another way, the lower proportion of thermoplastic binderin the thermoplastic mix, the more cost effective the final productbecomes. Accordingly, a preferred method according to the presentinvention is a method wherein the proportion of the particulate materialin the thermoplastic mix is greater than the propertion of thermoplasticbinder. Even though at elevated temperatures only a fraction of thethermoplastic mix assumes liquid form, the inventors have found thatthis is still sufficient to enable the thermoplastic mix to flow intoand fill the mould. Accordingly, a further preferred method according tothe present invention is a method wherein the heating of thethermoplastic binder is such that a fraction only of the thermoplasticmix assumes liquid form but is consistent with enabling thethermoplastic mix to flow.

Preferably the hybrid building products have a thermoplastic bindercontent of less than 30% by weight, more preferably from 1 to less than30% by weight. Preferably, the thermoplastic binder is present in anamount of at least 2% by weight, more preferably in an amount of atleast 3% by weight, most preferably at least 4% by weight. Preferably,the thermoplastic binder is present in an amount of up to 15% by weight,more preferably up to 10% by weight, most preferably up to 8% by weight.

Accordingly a preferred method according to the present invention is amethod wherein the proportion of thermoplastic binder is less than 30%by weight of the thermoplastic mix, more preferably less than 10% byweight of the thermoplastic mix.

When the proportion of thermoplastic binder is less than 10% by weightof a particulate mix including aggregate, sand and fine filler, theinventors have found that the thermoplastic binder in a hot hybridthermoplastic mix is in a liquid form that is flowable sufficient to betransferably from a holding hopper of a conventional concrete blockmaking machine and into the mould cavity therein.

Preferably, building products prepared by means of the method of thepresent invention have a flexural strength of at least 0.5 N/mm².Preferably, the flexural strength is at least 3 N/mm², more preferablyat least 4 N/mm², more preferably at least 5 N/mm², most preferably atleast 6 N/mm². Flexural strength is measured according to NEN 7014,“Nederlands Normalisatie Instituut” , 2^(nd) edition 8/1974.

In addition, it has been found that good compression strengths can beobtained by using the method of the present invention to preparebuilding products. Compression strengths which can be obtained are 5N/mm² or more, preferably 10 N/mm² or more, more specifically 15 N/mm²or more, measured according to ISO/R 836 of the European Federation ofManufacturers of Refractory Products as revised in 1990, PRE/R 14-1.

Unlike conventional thermoplastic materials but as with conventionalconcrete mixes containing natural materials including a cement binder,the hybrid thermoplastic mix of the invention requires compacting bydirect pressure and/or vibration by suitable pressing means to eliminateor at least substantially reduce undesirable voids which weaken thefinished product. One form of pressing means suitable for use in thisinvention comprises at least one compacting head. Accordingly, apreferred method according to the present invention is a method whereinthe thermoplastic mix is compacted by pressing and/or vibration.

Compaction may be achieved by any conventional means but is preferablyby lowering a compacting head on to the upper surface of the hybridthermoplastic mix in the mould cavity which exerts a force by directpressure and/or vibration. The compacting head may also be used forstripping. The resultant action of the applied pressure and/or vibrationis that the hybrid thermoplastic mix is compacted within the mouldcavity until the particles, i.e. sand, aggregates and fine fillers, areclosely packed with the thermoplastic binder in liquid form/phase actingas a lubricant to assist in closely packing the particles.

As the application of the compacting force is continued, the compactingforce acts primarily on the thermoplastic binder in liquid phaseenabling the binder to flow around and between the particulatematerials, including sand, aggregate and fine fillers, and to fill anyvoids there between.

Accordingly, a preferred method according to the present invention is amethod wherein the particulate material includes sand, aggregate andfine filler wherein prior to the pressing action the particles of thethermoplastic mix and thermoplastic binder are in a loosely packedarrangement with there being voids between the particles and theparticle being coated with a layer of thermoplastic binder and finefiller; a further preferred method being a method wherein the finefiller and thermoplastic binder coating lubricates the sand andaggregate particles to provide a product in which the particles are in aclosely packed arrangement with the voids being filled by thermoplasticbinder and fine filler.

The building products prepared by means of the present inventionpreferably have a void content of at most 3%, more preferably at most2.5%, most preferably at most 2.0%. The void content is determinedaccording to the “Standaard Regelgeving Advisering Wegenbouw”, 1995,test 67.

When the compacting forces are stopped, the mould is then raised fromthe pallet, with the compacting head, now acting as a stripping device,being held in stationary alignment and with the formed and shaped blockof compacted hybrid thermoplastic mix being left on the pallet. When themould has been raised clear of the formed block the compacting/strippinghead is also raised clear of the compacted hybrid thermoplastic mix. Theformed blocks of compacted hybrid thermoplastic mix is then conveyed outof the block making machine on the pallet on which they were formed.

The formed blocks may be allowed to cool on their own sufficiently toenable handling and packaging, i.e. under ambient conditions without anyadditional cooling being provided. However, this takes a long time andthe cooling process is ideally accelerated by subjecting the formedblocks to a cooling process, for example quenching with water, beforebeing conveyed into a racking station where they are allowed to coolsufficiently to enable handling and packaging. The benefit of subjectingthe blocks to a cooling process such as quenching is to solidify thethermoplastic binder close to the outside parts of the formed blockssuch that the shape of said blocks is maintained during subsequenthandling whilst most of the block remains in a plastic state.

In order to ensure that the thermoplastic binder remains in liquid formprior to being fed into the mould cavities, the hybrid thermoplastic mixis maintained at a desired elevated temperature by heating the walls ofone or more supply hoppers for the hybrid thermoplastic mix and/orinsulating against loss of heat from the or each supply hopper bylagging. Accordingly, a preferred method according to the presentinvention is a method wherein the thermoplastic binder is heated in asupply hopper such that the thermoplastic binder assumes liquid form toenable the thermoplastic binder mix to flow; and a more preferred methodis a method wherein the thermoplastic mix is heated in a supply hopperand maintained at the desired elevated temperature in the supply hopper.

Moreover, the mould cavities need to be held at a controlled temperaturerange to ensure correct compaction of the thermoplastic mix because lowmould cavity temperatures causes premature solidification of thethermoplastic binder resulting in poorly compacted products. Moreparticularly, the construction of mould boxes with multiple cavitiesresults in there being large masses of metal material forming the outerframe of the mould box that is sub-divided into smaller mould cavitiesby the use of thin metal divider plates. In use, and with continualcharging with hybrid thermoplastic mixer at elevated temperatures, thethin divider plates rapidly rise to a temperature close to that of themix itself. Whilst this rapid rise in temperature of the thin dividerplate ensures that there will be no premature solidification of thethermoplastic binder, preferably the divider plates may be cooled suchas to reduce any tendency towards sticking of the thermoplastic mix tothe divider plates and consequently ensure satisfactory strippingtherefrom.

It will be appreciated that the large masses of material forming theouter frame of the mould also form the side walls of the small mouldcavities around the perimeter of the mould. Even in use,and withcontinual charging with hybrid thermoplastic mixes at elevatedtemperatures, the large mass of the mould frame acts as a heat sink suchthat it never attains a temperature close to that of the mix itself.This can cause premature solidification of the thermoplastic binder inthe mix and consequentially produce poorly compacted products at leastin so far as their side walls are concerned. Accordingly, it isdesirable to heat the mould frame.

Again, with mould blocks having multiple cavities, the compacting headcomprises an array of stripper shoes, one for each mould cavity. Asthese stripper shoes are of low mass and, like the division plateswithin the mould cavity, in use rapidly attain a temperature which isclose to that of the hybrid thermoplastic mix itself due to beingcontinually charged with high temperature hybrid thermoplastic mixes.Whilst this ensures that there will be no premature solidification ofthe thermoplastic binder which would clearly be undesirable,advantageously the stripper shoes are cooled such as to reduce anytendency toward sticking of the hybrid thermoplastic mix to the shoes toensure satisfactory stripping therefrom.

Unlike other known processes using thermoplastic materials which rely onre-solidification of the thermoplastic material within a mould to ensurethe dimensional integrity of the finished product, the inventors havefound that the hybrid thermoplastic mixes of the invention do notrequire cooling within the mould cavities to solidify the thermoplasticbinder before it is ejected therefrom. Even when demoulded, the shaped,formed and fully compacted hybrid thermoplastic product remainsself-supporting when demoulded and may be allowed to cool and solidifyover a period of some hours or even days provided that no externalpressure is applied. However, the long time intervals needed forsufficient cooling may add undesired costs to the overall processbecause additional carrier plates, racks etc. would be necessary.

Accordingly, in another preferred embodiment of the invention, rapidcooling of the demoulded products is provided to considerably speed upthe cooling process, for example by way of immersion in a water bath ordrenching in water sprays.

The present invention further provides a building product obtainable bythe method of the present invention.

In order that the invention may be more fully understood, reference willnow be made, by way of example to the accompanying drawings, in which:—

FIGS. 1, 2, 4, 6, 7 and 8 are diagrammatic cross-sectional sideelevations through a pressing apparatus in various stages of carryingout a method of manufacturing a building product according to thepresent invention;

FIG. 3 is a plan view of a mould box comprising a plurality of mouldcavities and forming part of the pressing apparatus of FIGS. 1, 2, 4, 6,7 and 8;

FIG. 5 is a diagrammatic part-sectional view to an enlarged scalethrough an individual pressing means forming part of the pressingapparatus of FIGS. 1 to 4 and 6 to 8;

FIG. 9 is a diagrammatic view of the state of a hybrid thermoplastic mixprior to be pressed and compacted by the pressing apparatus of FIGS. 1to 8; and

FIG. 10 is a similar view to that of FIG. 9 showing the state of thehybrid thermoplastic mix in a building product which has been formed andshaped by pressing and compacting in the apparatus of FIGS. 1 to 8.

Referring to FIGS. 1 to 8 there is shown an apparatus for manufacturinga building product such as building block from a mix includingparticular material comprising fine particles in the form of sand andfiller, coarse aggregate particles and a thermoplastic binder. Thethermoplastic mix is heated in the apparatus at least to a temperatureat which the thermoplastic binder in the thermoplastic mix liquefies,the heated thermoplastic mix is subjected to a pressing process thatshapes the heated thermoplastic mix and the shaped heated thermoplasticmix is cooled to solidify the thermoplastic binder and form a buildingblock.

As shown in FIG. 1 to 6, the apparatus for manufacturing hybridthermoplastic blocks includes a heating and charging station (1), amoulding station (2) and cooling station (3) which are generallyindicated by the references (1), (2) and (3) respectively.

The heating and charging station (1) is shown in FIG. 1 and comprises asupply hopper (4) which is insulated against heat loss by lagging (5)and contains a hybrid thermoplastic mix (6) comprising sand and fillerfine particles, aggregate coarse particles and a thermoplastic binderconstituted by a thermoplastic material A thermoplastic binder that mayconveniently be employed is a bituminous-based binder, more convenientlyan asphaltenes-containing binder having a penetration of less than 15dmm. The filler can be any one or combination of ground minerals such aslimestone, flyash, furnace slag, furnace waste and slate. A slide drawer(7) is moveable in the directions indicated by the illustrated arrows(8) between upstream and downstream positions in which it is locatedbeneath the hopper (4) and above a mould frame (9) respectively. In theupstream position, the slide drawer (7) is charged with a predeterminedamount of hybrid thermoplastic mix (6) dispensed from the hopper (4). Astationary bottom member (10) is engaged by the slide drawer (7) in itsupstream position to retain the hybrid thermoplastic mix (6) in theslide drawer (7).

Downstream from the slide drawer (7) in the moulding station (2), themould frame (9) is positioned on a pallet (11) in the form of a boarddisposed immediately beneath pressing means constituted by an array ofcompacting and stripping heads in the form of shoes (12) which arealigned with complementary mould cavities (14) in the mould frame (8) asshown in FIG. 2. The shoes (12) are moveable between the positionsillustrated by the arrows (16) in which they are disposed above themould cavities (14) and in alignment therewith and positions in whichthey engage in the mould cavities (14).

The slide drawer (7) in FIG. 2 has moved into its downstream positionabove the mould frame (9) into which the charge of hybrid thermoplasticmix (6) has been dispensed. The thermoplastic mix (6) fills and somewhatoverflows the mould cavities (14) of the frame (9) and presents asurface (16′) to the shoes (12). The hybrid thermoplastic mix (6)assumes the shape of the mould cavities (14) but at this moment in timeis in an uncompacted state illustrated in FIG. 9 which will be referredto in more detail later.

The slide drawer is then moved back to its upstream position in theheating and charging station (1) where is it disposed beneath the hopper(4) to receive another charge of heated thermoplastic mix (6), as willbe apparent from FIG. 4.

FIG. 3 shows the construction of a typical mould frame (9) comprising anouter frame portion (20) and divider plates (21) that form the sidewalls of individual mould cavities (14). Within the overall mould frame(9) resides cavities (14 a), (14 b), and (14 c) differentiated in thatcavities (14 a) are formed with all four walls constructed from dividerplates (21), cavities (14 b) have three side walls constructed fromdivider plates (21) and one side wall constructed from the outer frame(20), and cavities (14 c) have two side walls constructed from dividerplates (21) and two side walls constructed from the outer frame (20).

The outer frame (20) is warmed by a flow of heated fluid in the form ofwater, oil or other liquid or gas supplied through a supply conduit (23)which is circulated around the outer frame (20) and out through the exitconduit (23 a). The flow of heated fluid through the outer frame (20)prevents intimate contact with what would otherwise be a cold surface byensuring that the surface of hybrid thermoplastic mix (6) is not cooledsuch as to cause localised re-solidification of the thermoplastic binderadjacent to wall areas (24).

Additionally, when the process has been in operation for some length oftime, the wall surfaces (25) are sufficiently cooled by causing acooling fluid to flow through dividers in the form of division plates(21) so that the surface of the hybrid thermoplastic mix (6) in contactwith the plates (21) does not stick to the plates (21). In the eventthat large format products are being made the number of division platesrequired will be low and could be omitted.

In FIG. 4, the shoes (12) are shown in their positions in which theyhave been lowered on to the hybrid thermoplastic mix (6) and into themould cavities (14). By applying pressure and/or vibration to the shoes(12), and optionally vibration to the underside of the pallet board(11), the hybrid thermoplastic mix (6) is compacted into the compactedstate and is now designated the reference (6 a) in FIG. 10, which willbe referred to in more detail later to form building blocks which areindicated by the reference (18) in FIG. 6.

The lower surface (28) of each shoe (12) (see FIG. 5) that comes intoclose contact with the heated hybrid thermoplastic mix (6) is maintainedat a temperature which is higher than ambient temperature but lower thanthe temperature of hybrid thermoplastic mix (6). This is achieved bycausing a flow of fluid such as water, oil or other liquid or gas at acontrolled temperature to pass through a flow passage (30) connected toinlet and outlet conduits (31) and (32) of the shoe (12). This ensuresthat when the shoes contact the thermoplastic mix (6) at the beginningof the pressing process and the first charge of hybrid thermoplastic mix(6) is pressed into the mould cavities (14), the lower surface (28) ofthe shoe (12) is sufficiently warmed by the flow of fluid. In this way,the upper surface of hybrid thermoplastic mix (6) is not cooled andlocalised solidification of the thermoplstic binder in the mix (6).which would have otherwise occurred due to contact with a cold surfaceis avoided. Moreover, when the process has been in operation for somelength of time, the temperature of the fluid flowing through the shoe(12) is sufficient to cool the upper surface of hybrid thermoplastic mix(6) that it does not stick to the surface (28) of the shoe (12).

Referring now to FIG. (6), with the shoes (12) held in stationaryalignment in the mould cavities (14) the mould frame (9) is raised to aposition in which it clears the tops of the blocks (18) thereby in theprocess ejecting (stripping) the blocks (18) from the mould cavities(14). The array of shoes (12) is then also raised in the direction ofthe upper head of the arrows 16 and away from the tops of the blocks(18). This enables the entire array of blocks (18) on the pallet board(11) to be conveyed downstream of the mould frame (9) for furtherprocessing and the mould frame (9) to be lowered back on to the palletboard (11), as shown in FIGS. 1, 2 and 4, to allow the cycle which hasjust been described to be repeated.

The blocks (18) on the pallet board (11) are then conveyed horizontallyupstream from the moulding station (2) to a cooling station (3) as shownin FIG. 7. In the cooling station (3), the blocks (18) on the palletboard (11) are located in a position above a tank (40) that is partiallyfilled with cold water (41). The pallet board (11) carrying the blocks(18) is then lowered into the tank (40) and on to a conveying means (42)such that the blocks (18) are completely immersed in the cold water (41)as shown in FIG. 8. The pallet board 11 carrying the blocks (18) is thenmoved by the conveying means (42) along the entire length of the tank(40). During immersion of the blocks (18) in the cold water (41), thethermoplastic binder in the blocks (18) is solidified at least in thearea adjacent to the side walls of the blocks (18) which stabilises theshape of the blocks (18) throughout any further movement of the palletboard (11). Then the pallet board (11) carrying the blocks (18) israised from the tank (40) and conveyed away to an optional rackingstation (not shown) where the blocks (18) are allowed to cool and thethermoplastic binder therein allowed completely to solidify.

Alternatively and as shown by dashed lines in FIG. 7, the blocks (18) onthe pallet board (11) are cooled by drenching with water sprayed fromabove through spraying jets (45) of a spraying apparatus (46). Whencooling of the blocks (18) is sufficient, the blocks (18) on the pelletboard (11) are conveyed from the cooling station (3) and treated asdescribed in the previous paragraph.

When complete solidification of the thermoplastic binder in the blocks(18) has occurred, the constituents of the thermoplastic mix (6 a)occupy the state which is shown in FIG. 10. Then the blocks (18) are fitto be subjected to secondary processing such as shotblasting, bushhammering etc. as hereinbefore referred to, before being packaged andshaped as required.

Referring to FIG. 9, it will be seen that the uncompacted hybridthermoplastic mix (6) comprises aggregate the particles (51), sandparticles (52), and a mixture of fine filler and thermoplastic binder(53) in a loosely packed arrangement. The proportion of thermoplasticbinder/fine filler (53) is in excess of that required to provide asingle molecular layer to the total surface area of aggregate (51), sand(52), and forms a relatively thick layer (53) of thermoplasticbinder/fine filler mixture around the aggregate particle (51) and sandparticles (52), including voids (54).

In FIG. 10 the voids (54) between the particles (51), (52) of theloosely packed, uncompacted thermoplastic mix (6) shown in FIG. 9 havebeen eliminated. Instead, the particles (51), (52) are disposed in aclosely packed arrangement produced by the compacting action of pressureand/or vibration. In this closely packed arrangement, the layer (53) ofthermoplastic binder/fine filler mixture surrounding each particle isreduced in thickness due to migration of some of the thermoplasticbinder/fine filler mixture (53) from around the particles (51), (52) tofill the voids (54) as indicated by the reference (53 a).

Although the invention has been particularly described it will beappreciated that various modifications may be made without departingfrom the scope of the invention as define in the appended claims. Forexample, the pressing apparatus may be of any other suitable kindconsistent with providing the required finished product. Moreover, air,applied by means of an air knife for example, may be used, instead ofwater, to cool the blocks (18) in the pallet board (11).

1. A method of manufacturing a building product from a mix includingparticulate material and a binder, characterized by the binder being athermoplastic binder which binder is an asphaltenes-containing binderhaving a penetration of less than about 15 dmm, comprising: heating themix including the thermoplastic binder at least to a temperature atwhich the thermoplastic binder in the mix liquefies; subjecting theheated thermoplastic mix to a pressing action that shapes the heatedmix; and cooling the shaped heated thermoplastic mix to solidify thethermoplastic binder and form the building product; wherein the heatedthermoplastic mix flows into at least one mould cavity defined by anouter mould frame and in that the outer frame is warmed to preventsolidification of thermoplastic mix adjacent to the outer mould frame;and further wherein the outer mould frame defines together with dividersan array of mould cavities and in that the dividers are cooled toprevent sticking of thermoplastic mix adjacent to the dividers.
 2. Themethod according to claim 1, wherein the pressing action is carried outby at least one compacting head and in that the compacting head issubjected to the action of a fluid which prevents sticking of the headto the thermoplastic mix during the pressing action.
 3. The methodaccording to claim 1, wherein the proportion of thermoplastic binder isless than about 30% by weight of the thermoplastic mix.
 4. The methodaccording to claim 3, wherein the proportion of thermoplastic binder isless than about 10% by weight of the thermoplastic mix.
 5. The methodaccording to claim 1, wherein following the pressing action the shapedheated thermoplastic mix is cooled by the action of water.
 6. The methodaccording to claim 5, wherein the heated shaped thermoplastic mix iscooled by immersion in water.
 7. The method according to claim 5,wherein the heated shaped thermoplastic mix is cooled by water sprays.